[DF] CAST not happening for certain GPU dtypes

[jdye64]

Is your feature request related to a problem? Please describe. We are seeing str literals be present in call.py, specifically the ReduceOperation. Really this shouldn't be happening. A str for example from the SQL clause TIMESTAMP '2022-06-16' should already be CAST to a timestamp64 instance by the time it reached reduce in ReduceOperation. This likely means that somewhere in the CAST logic there is an edge case missing where a filter is not catching certain GPU types to perform those CAST operations on them.

Describe the solution you'd like I would like to not be seeing str instances in Rex operations where CAST is involved.

Describe alternatives you've considered None

Additional context This really is more of a BUG than a feature but kind of both.